An Introduction
]] Fungi are a large group of organisms; they are quite distinct from other groups, unique in their behaviour and cellular organization. In what many people call a Tree Of Life, more properly a Phylogenetic Tree, fungi sit between - and are equal to - animals and plants. Given the size of this Kingdom, and the speed of the expansion of its description (see below), "An Introduction" to Fungi is likely to be woefully incomplete and short. For comparison, imagine "An Introduction To Animals" and how superficially it would cover each group of species, unless it were a large multi-volume text. Fungi Are... Like Animals Fungi are Eukaryotes, more closely related to the other two Eukaryiotic Kingdoms, plants and animals, than to Prokaryotes such as Bacteria and Archea. They are like animals in that they are heterotrophic, they cannot convert carbon dioxide into organic carbon compounds as plants do. Nor can they eat (ingest) prey items or food as animals do - they absorb their food from outside their bodies using a range of enzymes. Instead they are * biotrophic - when they form a mutualistic and long term symbiotic relationship with another organism * saprotrophic - that feed on non-living or dead material, animal waste, fallen logs, corpses of animals * necrotrophic - when they kill the host's cells and tissues as part of the feeding process. They fill diverse roles within ecological communities: decomposers, parasites and mutualists The Phylogenetic Tree of Life, shown above, refers only to extant species - species that are not extinct - and is constructed using analysis of RNA. Diverse Fungi is a large and diverse Kingdom; 99,000 species are known and, currently, about 12,000 more are found each year (Danby, 2019). Genetic analysis has shown that, contrary to outward appearance, right|thumb|A Russula mushroom, similar to [[Russula emetica, J Lacey 2019]] fungi are more closely related to animals than to plants. Estimates have put the total number of fungal species at 1.5 million. (Campbell et al, 2008) Humans make wide use of fungi's diversity, they are used in the manufacture of food and drink and in making drugs - the class of drugs called antibiotics revolutionised infection and disease control in the early to mid 20th century and became the main method of controlling bacterial infection in both humans and animals. Older Than Western Civilization, Larger Than a Blue Whale Whilst, initially, it might appear to be hyperbole to claim that individual mushrooms are older than civilization - more than one individual has been found that backs up the claim. When walking through a temperate wood (such as The Outwoods) it is easy to pass the many individuals of fungi without noticing, though perhaps one would notice the brightly coloured individuals, such the fly agaric (Amanita muscaria) pictured here. . Look a little more closely and there are many examples of fungi visible as you walk, often around the base of trees, on fallen logs or apparently attached to the trunks of trees, like a bracket, from which they take their name. In fact the bracket fungi are emerging from inside the trunk. fungi live in close association with a host species, often plants. Mushrooms are, of course, just the short lived and visible portions of much larger organisms that extend, in what are sometimes very large networks, through soil or other matter. Mycologists, scientists who specialise in fungi, refer to mushrooms and bracket fungi, as fruiting bodies. They are the visible parts, the apples and berries of a largely hidden fungal world. It is as if under the forest floor there are trees growing, pushing their way through the the soil and fallen leaves so that only the blossom and fruits are visible. Most of a fungus is hidden and the visible parts may only last a few days - though some do last for years. Some last for many years: one, an individual of Armillaria ostoyae has been found in Oregon; it is estimated to be over 2,000 years old and weigh "hundreds" of tonnes and similar examples are suspected to be relatively common (Brooker et al, 2017). Another individual, this time of Armillaria gallica was discovered in Michigan during the 1980s (Smith et al, 1992) though it was originally referred to as A. bulbosa and thought to be about 1,500 years old and weighing approximately 100 tonnes. This was studied again in 2017/18 and is now thought to be at least 2,500 years old and 400 tonnes (Anderson et al, 2018). These are the largest organisms of any kind that have been found so far; given that it is only since the advent of affordable genetic sequencing techniques that these extensive and ancient fungi have come to light, it seems inevitable that other examples remain to be discovered, perhaps much older and larger, . Adult Blue Whales (Balaenoptera musculus) incidentally, range in size from 73 to a mere 173 tonnes (Sears, and Perrin 2009). Uni and Multicellular A few species exist only as single celled yeasts, some as both yeasts and multi-cellular filaments - but many more only as filaments. The morphology of filamental fungi is varied and highly adapted to nutrient absorption. The filaments, called Hyphae, grow apically - from the tips only - and permeate the substrate in which they are absorbing nutrients in an interwoven structure called a myceleum. Hyphae are adapted to maximise absorption efficiency in the same way that mammallian intestines are adapted by being lined with villi and microvilli to maximise the surface area of the gut in contact with nutrients. In the case of hyphae, a single cubic centimetre of soil could contain 1 kilometre of hyphae with a surface area of 3 square metres ((Campbell et al, 2008). Hyphal growth is adapted to increasing length and not girth. As the tip grows, protoplasm moves forward from older parts of the hyphae. Older sections of hyphae differentiate, containing progressively larger vacuoles which eventually occupy most of the space within a hyphal compartment. The older areas also contain lipid energy reserves and crystalline structures called Woronin bodies. Some hyphae are divided by septa - cross walls - more regularly than others, though in the more regularly divided septate hypha, the septa have pores through which protoplasm and organelles can migrate. Septate hyphae are compartmentalised cells, rather than individual cells. In contrast, coenocitic hyphae only have septa to separate fruiting bodies or older areas. Hyphae contain eukaryotic cell organelles or their equivalents which are familiar to animal and plant biologists, and have elements that resemble both plant and animal cells. Septate hyphae are often multinucleic in the apical regions which are actively growing and one or two in each of the non-growing sealed compartments behind. In contrast, the aseptate fungi have, in effect, much longer compartments with many nuclei. Next Page